Conventionally, there is an image reading apparatus which reads an image on photographic printing paper or a magazine using an image reading unit having a plurality of photoelectric conversion element arrays that are linearly arranged.
Since the image reading apparatus has the plurality of photoelectric conversion element arrays arranged linearly, the photoelectric conversion element arrays have joints therebetween, and a read image has discontinuous portions corresponding to the joints. However, the size of the gap at each joint is as small as about 60 μm in the current manufacturing technique. When an image on photographic printing paper or a magazine is to be read using a general 1.times. lens as ever, such a 60-μm joint is negligible relative to the original size.
However, when a function of reading a transparent original such as a photographic film is to be imparted to an image reading apparatus, joints pose a problem. To read and display a small fine image of a photographic film, high-resolution photoelectric conversion element arrays are often used, and a read image is enlarged when displayed in many cases. For this reason, when the resolution of photoelectric conversion element arrays is, e.g., 2,400 dpi, a discontinuous portion/portions of 60-μm gap which corresponds to about six pixels at a resolution of 2,400 dpi is/are formed in an image. The discontinuous portion/portions is/are especially noticeable when the image is enlarged and displaying or printing an enlarged image.
Additionally, the image reading apparatus which reads a transparent original using photoelectric conversion elements has a poorer resolution at an end portion than at the central portion with respect to the main scanning direction because of its optical system structure. Hence, a transparent original is generally read near the central portion.
Recently, however, an image reading apparatus using an contact type image read sensor which contacts with an original glass plate has been developed in order to make the apparatus thin and compact. When a photographic film is to be read by attaching a transparent original irradiation unit to such an apparatus, the upper and lower edges of the film cannot be held by a film holder, hence, the film must be placed directly on the original glass plate while the transparent original irradiation unit is placed on the film. In this case, even a very small shift of the film from the focal point of the contact type image read sensor can result in a decrease in resolution because of a small depth of field.